1. Field of the Invention
The present invention relates to an image display apparatus and in particular, to a small-size light in weight spectacles-type image display apparatus.
2. Description of the Related Art
Conventionally, various types of image display apparatus have been suggested for deflecting a beam modulated by a video signal for horizontal scan and vertical scan, so that the scan beam is projected by a projection optical system into a pupil of a user so as to be focused on a retina to display a scanned image. These image display apparatuses employ a method so that a light emitted from a light source is effectively introduced into eyes, realizing an image display apparatus of a low power consumption.
For example, Japanese Patent Publication (unexamined) No. A-4-100088 [1] discloses a direct view type image display apparatus using an acousto-optical deflector for horizontal scan and a galvanometric mirror for vertical scan of a laser beam, and a focusing system constituted by two lenses.
Moreover, Japanese Patent Publication (unexamined) No. A-6-138499 [2] discloses a direct retina type scan display apparatus as an image display apparatus built in spectacles. FIG. 6 shows a configuration of this direct retina type scan display. This direct retina type scan display includes: a reflector 101 such as spectacle lenses, an optical scanner 102, a fiber relay 104, a laser source 105, and a frame 106. A laser beam emitted from the optical scanner 102 provided on a bow of the frame 106 is reflected by the reflector 101 so as to be projected into a pupil.
Moreover, Japanese Patent Publication (unexamined) No. A-6-121256 [3] discloses a direct retina scan type display apparatus using a planer type image sensor. FIG. 7 shows an optical system of this direct retina scan type display apparatus. This direct retina scan type display apparatus includes: an optical wave-guide channel 201, diffraction optical element 202, an optical wedge 203, a deflection system 204, a laser/modulator 205, and an electron circuit 206. The light beam from the laser/modulator 205 is deflected/scanned by the deflection system 204 and re-oriented by the planer type image sensor having the optical wedge 203, the optical wave-guide channel 201, and the diffraction optical element 202, so that the light beam is directed toward an operator's eye so as to form a virtual image on the retina.
Furthermore, a virtual image type display apparatus has been suggested in the proceeding of SPIE, No. 2464, 1953, pp. 2 to 13 [4]. FIG. 8 shows a configuration of an optical system of this virtual image type display apparatus. This virtual image type display apparatus includes: a mirror 301, a beam splitter 302, and an optical scanner 303. This apparatus has an optical system identical to the one used in a conventional liquid crystal display apparatus. The light emitted from the optical scanner 302 is reflected by the mirror 101 and introduced via the beam splitter 302 into the pupil.
However, these conventional image display apparatuses have various problems as follows.
The direct view type image display apparatus disclosed in Document [1] employs an acousto-optical deflector. This increases the entire apparatus size and cannot reduce the size and weight.
On the other hand, the direct retina scan display apparatus disclosed in Document [2] can be built in spectacles but has a disadvantage that a comparatively large scan or deflection angle is required for the laser beam shift distance between the light source and the retina.
In order to improve this disadvantage, the applicant of Document [2] has suggested the direct retina scan display apparatus using the planer type image sensor disclosed in Document [3] and shown in FIG. 7. However, this apparatus uses a multi-reflection by total reflection of light in the wave-guide channel 201 of the planer type image sensor. Accordingly, the optical wave-guide channel should have a sufficient thickness so that the light finally diffracted by the diffraction element to be introduced into the eye is not overlapped by the light reflected in the wave-guide channel. For example, in order to display an image with 30 degrees as the angle of visibility, the diffraction optical element 202 has a diameter of about 1 cm at 2 cm from the eye. In order to prevent overlap with an adjacent reflected light, the optical wave-guide channel 201 needs to have a thickness of about 3 mm assuming 60 degrees for the final incident angle of the reflected light. This increases the weight of the lens portion of the spectacles, thereby causing the spectacles to be too heavy for the user.
Moreover, the virtual image type display apparatus disclosed in Document [4] and shown in FIG. 8 includes an optical system identical to the one used in a conventional liquid crystal display apparatus having the mirror 301 and the beam splitter 302. This significantly increases the entire apparatus size and the beam splitter 302 decreases the light quantity and does not effectively use the light.